Turbine systems are widely utilized in fields such as power generation. A typical gas turbine includes a compressor section, a combustion section downstream from the compressor section and a turbine section downstream from the combustion section. At least one shaft extends at least partially axially through the gas turbine. A generator/motor is coupled to the shaft at one end. The compressor section includes an inlet defined at an upstream end of the compressor section. The combustion section generally includes a casing and a plurality of combustors arranged in an annular array around the casing.
Each combustor includes an end cover that is connected to the casing. At least one fuel nozzle extends generally axially downstream from the end cover and at least partially through a cap assembly that extends radially within the combustor downstream from the end cover. An annular liner such as a combustion liner and/or a transition piece extends downstream from the cap assembly to at least partially define combustion chamber and/or a hot gas path through the combustor. The liner generally terminates at a point adjacent to an inlet of the turbine section. In certain gas turbine designs, a series of cross fire tubes extend through the liner and the casing between each or some of the plurality of combustors to define a flow path between each adjacent combustor. A spark plug is disposed at or adjacent to the combustion chamber of one of the plurality of combustors.
During start-up or light off of the combustion section, the generator/motor turns the shaft to drive the compressor section. A working fluid such as air is ingested through the inlet of the compressor section and is progressively compressed as it flows through the compressor section towards the combustion section. The compressed air is routed into the combustion section casing where it is distributed to the individual combustors of the combustion section. The compressed air is mixed with a fuel to form a combustible mixture within the combustion chamber of each combustor. The spark plug is triggered to ignite the combustible mixture within the respective combustor. A flame then travels through the cross fire tubes to light off the adjacent combustors in series until each combustor of the combustion section is lit.
The spark plug and the cross fire tubes as a system are generally effective for lighting off the combustion section of the gas turbine. However, various issues with cross fire tube ignition systems, particularly in combustors utilizing late lean technology, may increase cost and may place undesirable restrictions on combustion designers. For example, such issues may include varying thermal growth rates of the adjacent combustors which may lead to leakage around the cross fire tubes, the potential for cross-flow through the cross fire tubes of adjacent combustors after light off, purging of the cross fire tubes after a blow out of one or more of the combustors, re-lighting a combustor after a blow-out event and/or cooling of the cross fire tubes during operation of the gas turbine. In addition, various current spark plug designs may be breach loaded through the casing and/or through the end cover, thereby creating an additional potential leakage area. Accordingly, an improved system for lighting off the combustors of the gas turbine would be useful in the art.